Codebreaking expert and book author Helen Fouché Gaines created a crypto challenge that is unsolved to this day.
Magnus Ekhall from Sweden has solved my Playfair challenge from April 2019. With only 30 letters, this ciphertext is the shortest of its kind ever broken.
A US radio station and a US non-profit organisation have received letters that look like code messages. Can a reader decipher them?